A method to evaluate quality of PWHT of welds in tubular panels made of Cr-Mo steel in once through supercritical boiler

FIELD OF INVENTION
[001] The present invention relates to a method of evaluating the 5 quality of Post-Weld Heat Treatment (hereinafter referred to as PWHT) of butt welds of Cr-Mo steel present in tubular panels of high pressure high temperature steam generators. This invention in particular is directed to a method to evaluate quality of PWHT of welds in tubular panels made of Cr-Mo steel in once through 10 supercritical boiler.
BACKGROUND OF THE INVENTION
[002] Background description includes information that may be 15 useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
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[003] Fossil fuel fired boilers are widely used for generation of power in thermal power plants. The boiler is the chief element in thermal power stations where the conventional fossil fuel is burnt and the heat of combustion is used to convert water into steam which then turns the turbine leading to generation of electricity. The fuel is 25 burnt in a furnace whose walls are made of tubular panels referred to as water walls. A typical tubular panel consists of tubes and fins welded alternately. Water runs inside the tube and the heat of combustion is transferred to the water across the tube walls. These tubular panels are fabricated from smaller panels and many weld 30 joints connect the smaller panels to produce a large interconnected
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assembly of panels that form the water walls. The water walls for a typical once through supercritical boiler consists of tubes that are inclined at an angle to the horizontal and hence they are referred to as spiral wall panels.
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[004] The water wall materials are so chosen to ensure a good creep life at the operating environment. For this purpose, these are normally built of Cr-Mo steels which are known to possess good creep strength on account of significant alloy additions. The shorter panels have to be joined by way of welding to form large 10 interconnected assembly of panels that form the water walls. The butt welds made between one tubular panel and another have to be subjected to a proper PWHT scheme in order to ensure the estimated creep strength. If there are deficiencies in PWHT, then it might have a serious impact on the service life of the components 15 as these welds are likely to fail in a premature manner. Hence, the quality of the PWHT performed in these welds have to be evaluated before commencing the operation of the boiler. In case deficiencies in PWHT is detected, the same has to be overcome by a re-PWHT as warranted by the situation. 20
[005] Presently, there are no standard methods available to assess the quality of PWHT of the tubular butt welds made in Cr-Mo steels in the tubular panels of once through supercritical boiler. Although, the measurement of hardness using a portable hardness tester after 25 PWHT can, to some extent throw light in this direction, it cannot be considered as a fool proof method as the measurements are likely to be influenced by several factors like the extent of surface preparation, operator errors like incorrect positioning of the indentor, incorrect selection of spot for measurement, existence of 30
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gradients in the measured values along the thickness of the weld, absence of an established conversion method to convert the values measured in portable hardness scale into bench hardness etc.
[006] To overcome these problems, in the present invention, a 5 method of assessing the PWHT quality of tubular butt welds of spiral wall panels of once through supercritical boilers is disclosed.
PRIOR ART SEARCH
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[007] Some prior arts may be discussed herein-under.
[008] US Patent US 20100092798 A1 describes a high-quality submerged arc weld metal for 1.25 Cr-0.5 Mo steel that is obtained by carrying out multi-pass welding in a submerged arc welding 15 process with a solid wire and a bonded flux being combined together. Further, the strength mismatch with the base material does not occur even after a Post Weld Heat Treatment is carried out for a short time to a long time, and which has high ductility as well as having no weld defect. Whereas this proposed invention discloses 20 a method for assessing the quality of welds made of Cr-Mo steel in supercritical boiler tubular panels after PWHT and to state whether the weld has received adequate PWHT or not.
[009] Chinese Patent CN 102419290 B discusses an improved 25 method for determining the strength of a laser welded maraging steel weldment after PWHT based on the ratio of hardness distribution found in the HAZ and the weld metal. But, the present invention pertains to the method of evaluation of quality of PWHT
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carried out in weld joints in tubular panels of once through supercritical boilers.
[010] Chinese Patent CN 102134822 B provides a method for enabling the online post weld heat treatment of rail welded joints 5 whereas this invention concerns the method of evaluation of the PWHT quality of the welds made of Cr-Mo steel present in tubular panels of once through supercritical boiler.
[011] Indian Patent 265906 describes the method of evaluation of 10 heat treatment effectiveness of ferromagnetic materials in general by way of measurement of magnetic coercive force in a selected area. But, this subject invention specifically relates to the method of assessing the PWHT quality of the welds made of Cr-Mo steel in tubular panels of once through supercritical boiler. 15
[012] WIPO Patent Application WO/2015/061487 discloses a method for characterizing material condition by employing a system that includes an electromagnetic sensor, impedance instrument and processing unit. Our invention is different in the sense that it 20 provides a method for evaluation of PWHT quality of butt welds in tubular panels that form a part of once through supercritical boiler.
[013] None of the above can fulfill the requirements of the present invention, for which it is designed. 25
OBJECTS OF THE INVENTION
[014] An object of the invention is to propose a method to evaluate 30 quality of PWHT of welds in tubular panels made of Cr-Mo steel in once through supercritical boiler.
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[015] Another object of the invention is to propose a method to evaluate quality of PWHT of welds in tubular panels made of Cr-Mo steel in once through supercritical boiler which helps in detecting those welds that are not satisfactorily post weld heat treated.
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[016] Still another object of the present invention is to provide a method to evaluate quality of PWHT of welds in tubular panels made of Cr-Mo steel in once through supercritical boiler which is simple.
[017] These and other objects and advantages of the present 10 invention will be apparent to those skilled in the art after a consideration of the following detailed description taken in conjunction with the accompanying drawings in which a preferred form of the present invention is illustrated.
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SUMMARY OF THE INVENTION
[018] One or more drawbacks of conventional systems and process are overcome, and additional advantages are provided through the apparatus and a method as claimed in the present disclosure. 20 Additional features and advantages are realized through the technicalities of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered to be part of the claimed disclosure.
[019] According to the invention, a method for evaluating the 25 quality of PWHT of weld joints present in tubular panels of once through supercritical boiler is disclosed. This method is capable of fully estimating the sufficiency of PWHT undergone by these welds. The invented method is significantly advantageous compared to the portable hardness measurement method which suffers from huge 30
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drawbacks like estimation of surface level hardness only, proneness to severe errors on account of sensitiveness of the positioning of the hardness indentors over the test surface and inadequate surface preparation etc. The importance of the method lies in the fact that the service life of the welds is dependent to a large extent on the 5 extent of effectiveness of PWHT to which the welds were subjected to.
[020] The tubular panels of once through supercritical boilers comprises of tubes welded with fins alternately. Tubular panels of smaller length are fabricated at shops and they are further welded 10 together at site to form huge assembly of tubular panels. The length and width of the panels are as per the design of the boiler. The weld joints connecting the tubular panels have to be made to achieve the required length of the membrane water wall panels at different locations and at different elevations in a boiler. Subsequent to 15 welding, the PWHT has to be carried out for both the tubular butt welds connecting the smaller panels to form the larger assembly of panels. The PWHT is performed by any of the known local PWHT techniques which includes the flexible ceramic pads or finger element resistance heating elements or induction coil heating 20 methods.
[021] After PWHT is carried out, the magnetic coercive force (MCF) of the butt welds weld joints in the tubes present in the tubular panel are measured in four locations circumferentially. The average of the four measurements made in the tubular butt welds is are 25 averaged. If the average of the MCF value is found to be less than or equal to a cutoff value, then the PWHT quality of the concerned weld joint is said to be satisfactory. If not, then the PWHT quality of the weld joint is not satisfactory and the PWHT might have to be repeated to ensure that the weld metal receives adequate tempering. 30
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After repeat PWHT, the average MCF value of the weld is again measured as stated earlier and the values are checked against the cutoff value whereby the PWHT quality of the weld is evaluated. The cutoff values are arrived at by performing an experimentation in lab scale. 5
[022] Various objects, features, aspects, and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components. 10
[023] It is to be understood that the aspects and embodiments of the disclosure described above may be used in any combination with each other. Several of the aspects and embodiments may be combined to form a further embodiment of the disclosure. 15
[024] The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by 20 reference to the drawings and the following detailed description.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
[025] The illustrated embodiments of the subject matter will be 25 best understood by reference to the drawings, wherein like parts are designated by like numerals throughout. The following description is intended only by way of example, and simply illustrates certain selected embodiments of devices, systems, and
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processes that are consistent with the subject matter as claimed herein, wherein:-
Figure 1 shows: Cross sectional view of tubular panels of once through supercritical boilers 5
Figure 2 shows: Schematic sketch showing butt weld joints present in tubular panels of once through supercritical boilers
Figure 3 shows: Schematic sketch of magnetic coercive force measuring Instrument 10
Figure 4 shows: Schematic sketch of a pipe weld and the method of sectioning it.
Figure 5 shows: Schematic sketch of method of carrying out magnetic coercive force measurements in butt weld joints present in tubular panels of once 15 through supercritical boilers.
[026] The figures depict embodiments of the disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods illustrated herein 20 may be employed without departing from the principles of the disclosure described herein.
DETAIL DESCRIPTION OF THE PRESENT INVENTION WITH REFERENCE TO THE ACCOMPANYING DRAWINGS OF PREFERRED EMBODIMENTS 25
[027] While the embodiments of the disclosure are subject to various modifications and alternative forms, specific embodiment thereof have been shown by way of example in the figures and will
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be described below. It should be understood, however, that it is not intended to limit the disclosure to the particular forms disclosed, but on the contrary, the disclosure is to cover all modifications, equivalents, and alternative falling within the scope of the disclosure. 5
[028] According to the invention, there is disclosed a method for assessing the quality of PWHT of butt welds made in tubular panels of once through supercritical boilers. These tubular panels comprise of alternately placed tubes and fins. The tube size, fin size and the length and width of the tubular panels are decided as per 10 the design of the boiler. The tubes and fins of the supercritical boilers are quite commonly made of Cr-Mo steels so as to ensure the desired creep strength of the boiler. The general cross sectional view of these panels is shown in figure 1. The tubes (1) are welded with fins {(2), (4)} to form the tubular panel. These panels are first 15 fabricated to transportable sizes in the shop floors and later on have to be welded at power plant erection sites to form an assembly of panels for functioning of the boiler. The weld joints in a typical tubular panel are schematically represented in figure 2. The weld joints (3) connecting two tubular panels are made by suitable 20 welding process. The welding and subsequent PWHT operations for joining these panels are carried out at site conditions as per the welding procedure specification (hereinafter referred to as WPS) established for this purpose. Since, the welding and PWHT are carried out at site conditions where there could be some not-so-25 easily accessible locations, there could be some chances of manual errors to creep in due to which the weld might not receive adequate tempering effect in the PWHT operation. The insufficiently post weld heat treated weld joints could subsequently fail prematurely during
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service. This is because insufficient PWHT will not guarantee the required levels of ductility and the desirable microstructure in the weld metal. Hence, there exists a need for evaluating the extent of effectiveness of the PWHT operation that the butt welds (schematically shown as (3) in figure 2) connecting the various shop 5 manufactured panels receive.
[029] This invention precisely describes the method of evaluating the effectiveness of PWHT operation and thereby the quality of weld joints after PWHT. The magnetic coercive force (hereinafter referred 10 to as MCF) property of the weld is a good reflector of the extent of PWHT received by the weld joints. An instrument that is openly available in the market called Magnetic Structurescope is used for measuring the MCF of the tubular butt welds connecting the various shop manufactured panels. The schematic sketch of the 15 ‘Magnetic Structurescope’ is shown in figure 3. The instrument comprises of an electronic measuring base (5) which houses the electronic circuitry that is responsible for calculation of MCF of the target material. The base (5) has a digital display (6) in which is displayed the MCF of the material in units of Ampere/centimeter 20 (A/cm). The base (5) is connected to the measuring probe (7) comprising of a pair of magnetizing pole tips (8). When the measuring probe (7) is placed over the target material in such a way that the magnetizing pole tips (8) are in contact with the area of the target material whose MCF is to be measured and the instrument is 25 energized, the MCF value of the region of target material is computed and is shown in the digital display (6) available in the base (5) of the instrument. Typically, for measuring the MCF of weldments, the measuring probe (7) is placed in such a way that
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both the magnetizing pole tips (8) are seated on the weld area only and not placed across the weld in the heat affected zones.
[030] The MCF values of the tubular butt welds are measured after PWHT. If the MCF value is below a cutoff limit, then the PWHT 5 quality of the weld joint is said to be satisfactory and the PWHT is deemed to be effectively performed. If the MCF value of the weld joint is higher than the cutoff limit, then the PWHT quality of the tubular butt welds connecting the panels is said to be not satisfactory and leads to the conclusion that the PWHT of the welds is not effectively 10 performed. The cutoff limit for deciding the PWHT effectiveness is derived by performing an experimentation involving various PWHT cycles in a lab scale as described below. This exercise is performed before going for the site application concerning the butt welds in the tubular panels of once through supercritical boilers. 15
[031] Two pipes belonging to the Cr-Mo classification of steel are taken and butt welded using the same WPS followed for welding the joints connecting the tubular panels at site. The pipe weld is then cut in a transverse manner into ‘n’ number of convenient segments. 20 This is schematically shown in figure 4. The weld joint made between the two pipes is shown as (9) in figure 4. The cutting lines are shown as dashed lines in this figure. After cutting the pipe weld into ‘n’ number of segments, the MCF value of the each of the pipe weld segment is measured in the as-welded condition using the 25 magnetic structurescope instrument as described earlier. The average of the MCF values of each of the segment is then referred to as Mw. Prior to cutting the pipe weld into ‘n’ number of segments, a small transverse cut section of the weld is extracted and the hardness of the weld is examined in a minimum of twelve spots 30
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covering the entire thickness of the weld. These hardness values are taken only in the weld zone and not in the adjacent heat affected zones. The average of all these hardness values is then referred to as the As-welded hardness of the pipe weld, denoted as Hw. After determining the average MCF value (Mw) and average hardness 5 value (Hw) of the pipe weld segment in the as-welded condition, each of the ‘n’ number of pipe weld segments is subjected to PWHT cycles involving ordered variations of soaking temperature and soaking time. After completion of PWHT in each of the ‘n’ number of weld segments, the MCF value of each of the weld segments is again 10 measured after PWHT as had been done earlier before PWHT. The average of all the MCF values measured in each of the weld segments after PWHT is then calculated and denoted as Mp. After measurement of MCF, the hardness of each of the pipe weld segment after PWHT is determined by extracting a small cut section 15 of weld and by following the same method as had been followed for determining the as-welded hardness of the pipe weld. The average of the hardness values determined in each of the ‘n’ number of pipe weld segments is calculated and determined as Hp.
[032] The percentage reduction of MCF of the each of the pipe weld 20 segment is calculated as {(Mw – Mp)/Mw} X 100. Similarly, the percentage reduction of hardness of each of the pipe weld segment is calculated as {(Hw – Hp)/Hw} x 100. Then, the percentage reduction of MCF is plotted as a graph against the percentage reduction of hardness calculated for each of the pipe weld segments. 25
[033] A regression equation of the following form describing the relationship between these two quantities is then derived using statistical techniques.
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y = f(x); where,
‘y’ refers to the percentage reduction of MCF of weld segments after PWHT
‘x’ refers to the percentage reduction of hardness of weld segments after PWHT 5
[034] It is to be ensured that the equation mentioned above i.e. y = f(x) is the equation of best fit for the quantities mentioned above.
[035] The desired hardness (Hd) of the weld after PWHT is to be selected which typically lies in the range of 250 – 295 HV (Hardness 10 measured in Vickers scale). This desired hardness of the weld is referred to as ‘Hd’. Then the following sequential calculation steps are followed.
(i) Calculate x1 = {(Hw – Hd)/Hw} x 100
(ii) Calculate y1 = f(x1) 15
(iii) Calculate Md = {(100 – y1)/100} x Mw
[036] Now, Md calculated in step (iii) above represents the cut-off value of MCF of weld that distinguishes the weld that is subjected to an insufficient PWHT to a weld that had received adequate PWHT. For applying this result for assessing the PWHT quality of butt welds 20 of tubular panels, the following procedure is followed.
[037] The tubular panels are welded at site conditions using the established WPS. The PWHT operation is then performed in the tubular butt welds after welding. After PWHT, the MCF value of a 25 tubular butt weld is measured at four locations (P1), (P2), (P3) and (P4) as shown in figure 5 using the Magnetic Structurescope instrument. The locations (P1) and (P2) are chosen in the butt weld
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above the fin connecting the tubes and locations (P3) and (P4) are chosen in the same tubular butt weld below the fin connecting the tubes as shown in figure 5. The MCF values taken in the four locations are then averaged. If the average MCF value measured in a tubular butt weld as mentioned above, exceeds the cutoff limit 5 ‘Md’ derived above, then it is said that the PWHT quality of the weld is not satisfactory. This indicates that the weld had received insufficient tempering effect during the PWHT. On the other hand, if the average MCF value measured in a tubular butt weld connecting two panels is found to be lesser than or equal to the 10 cutoff value ‘Md’, then it is concluded that the PWHT quality of the tubular butt weld is satisfactory and that the PWHT had been adequately provided for the welds.
[038] Each of the appended claims defines a separate invention, which for infringement purposes is recognized as including 15 equivalents to the various elements or limitations specified in the claims. Depending on the context, all references below to the "invention" may in some cases refer to certain specific embodiments only. In other cases, it will be recognized that references to the "invention" will refer to subject matter recited in one or more, but 20 not necessarily all, of the claims.
[039] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or 25 in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified 30
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thus fulfilling the written description of all groups used in the appended claims.
[040] The significant advantages of this method over the conventional method of using portable hardness testers is listed 5 hereinbelow:-
(A) The true quality of the weld is assessed in its entirety as against the portable hardness measurement method where the measurements are made only in selected locations of the weld and the spot of hardness measurement is of the order of 10 few microns. The hardness measurements are surface measurements only whereas the MCF measurements are volumetric measurements which reflects the true state of the weld material.
(B) Very good accuracy of measurement is ensured in the case of 15 MCF measurements as there is no requirement of weld surface preparation or operator skill, whereas good surface preparation and operator skill is an essential requisite for portable hardness measurement.
(C) The time of MCF measurement is also relatively short 20 compared to the portable hardness measurement as the latter method calls for meticulous surface preparation. Hence, the cycle of time of inspection of welds is drastically reduced in the case of MCF measurements.
[041] It will be understood by those within the art that, in general, 25 terms used herein, and especially in the appended claims (e.g., bodies of the appended claims) are generally intended as “open” terms (e.g., the term “including” should be interpreted as “including but not limited to,” the term “having” should be interpreted as
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“having at least,” the term “includes” should be interpreted as “includes but is not limited to,” etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is 5 present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases “at least one” and “one or more” to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles 10 “a” or “an” limits any particulars claim containing such introduced claim recitation to inventions containing only one such recitation, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an” (e.g., “a” and/or “an” should typically be interpreted to mean “at 15 least one” or “one or more”); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should typically be interpreted to mean at least the recited 20 number (e.g., the bare recitation of “two recitations,” without other modifiers, typically means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogues to “at least one of A, B and C, etc.” is used, in general such a construction is intended in the sense one having skill in the 25 art would understand the convention (e.g., “a system having at least one of A, B and C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, etc.). In those instances where a convention analogous to “at least one of A, B, or 30
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C, etc.” is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (e.g., “a system having at least one of A, B, or C” would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C 5 together, etc.). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For 10 example, the phrase “A or B” will be understood to include the possibilities of “A” or “B” or “A and B”.
[042] The above description does not provide specific details of manufacture or design of the various components. Those of skill in the art are familiar with such details, and unless departures from 15 those techniques are set out, techniques, known, related art or later developed designs and materials should be employed. Those in the art are capable of choosing suitable manufacturing and design details.
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[043] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. It will be appreciated that several of the above-disclosed and other features and frnctions, or alternatives thereof, may be combined into other systems or applications. 25 Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may subsequently be made by those skilled in the art without departing from the scope of the present disclosure as encompassed by the following claims. 30
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[044] The claims, as originally presented and as they may be amended, encompass variations, alternatives, modifications, improvements, equivalents, and substantial equivalents of the embodiments and teachings disclosed herein, including those that 5 are presently unforeseen or unappreciated, and that, for example, may arise from applicants/patentees and others.
[045] While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those 10 skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.

WE CLAIM:

1) A method to evaluate quality of PWHT of welds in tubular panels made of Cr-Mo steel in once through supercritical boiler wherein the tubes are made of ‘Cr-Mo’ Steels, the 5 method comprises of the following steps
- determining the cutoff value of MCF (Magnetic Coercive Force) that is derived by conducting an experimentation in lab scale involving a butt-welded pipe that is subjected to a series of PWHT cycles involving ordered variation of 10 soaking temperature and soaking time of PWHT and plotting the relationship between the percentage reduction of MCF against the percentage reduction of hardness of the pipe welds,
- measurement of the MCF value of the tubular butt weld 15 present after PWHT in atleast four positions all long the circumference of the tubular butt welds and averaging to obtain the final measured value of MCF of weld,
- if the final measured MCF value is higher than the cutoff value of MCF derived in the lab scale experimentation, 20 then the PWHT quality of the welds are considered not satisfactory and indicates that PWHT is not effective,
- if the final measured MCF value is lesser than or equal to the cutoff value of MCF derived in the lab scale experimentation, then the PWHT quality of the welds are 25 considered satisfactory and indicates that PWHT is effective.
2. The method to evaluate quality of PWHT of welds in tubular 30 panels made of Cr-Mo steel in once through supercritical
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boiler as claimed in claim 1, wherein two pipes of Cr-Mo Cr-Mo steel are butt welded followed by cutting the pipe weld in a transverse manner into ‘n’ number of segments, wherein the MCF value of each of the pipe weld segment is measured in the as–welded condition, in which average of the MCF values 5 of each of the segment is Mw.
3. The method to evaluate quality of PWHT of welds in tubular panels made of Cr-Mo steel in once through supercritical boiler as claimed in claim 1 or 2, wherein prior to cutting the 10 pipe weld into ‘n’ number of segments, a small transverse cut section of the weld is extracted and the hardness of the weld is examined in atleast twelve spots covering the entire thickness of the weld, in which average of all hardness values is the as-welded hardness of the pipe (Hw). 15
4. The method to evaluate quality of PWHT of welds in tubular panels made of Cr-Mo steel in once through supercritical boiler as claimed in claims 1-3, wherein after determining the average MCF value (Mw) and average hardness value (Hw) of 20 the pipe weld segment in the as-welded condition, each of the ‘n’ number of pipe weld segments is subjected to PWHT cycles involving ordered variations of soaking temperature and soaking time.
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5. The method to evaluate quality of PWHT of welds in tubular panels made of Cr-Mo steel in once through supercritical boiler as claimed in claim 1-4, wherein after completion of PWHT in each of the ‘n’ number of weld segments, the MCF value of each of the weld segments is again measured after 30
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PWHT and the average of all the MCF values measured in each of the weld segments after PWHT is then determined and denoted as Mp.
6. The method to evaluate quality of PWHT of welds in tubular 5 panels made of Cr-Mo steel in once through supercritical boiler as claimed in claim 1-5, wherein after measurement of MCF, the hardness of each of the pipe weld segment after PWHT is determined by extracting a small cut section of weld and the average of the hardness values determined in each of 10 the ‘n’ number of pipe weld segments is determined as Hp.
7. The method to evaluate quality of PWHT of welds in tubular panels made of Cr-Mo steel in once through supercritical boiler as claimed in claim 1-6, wherein the percentage 15 reduction of MCF of the each of the pipe weld segment is determined as {(Mw – Mp)/Mw} X 100, the percentage reduction of hardness of each of the pipe weld segment is determined as {(Hw – Hp)/Hw} x 100; the percentage reduction of MCF is plotted as a graph against the percentage 20 reduction of hardness determined for each of the pipe weld segments.
8. The method to evaluate quality of PWHT of welds in tubular panels made of Cr-Mo steel in once through supercritical 25 boiler as claimed in the claims 1-7, wherein the desired hardness (Hd) of the weld after PWHT is to be selected which typically lies in the range of 250-295 HV followed by determination of
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X1= [(Hw-Hd)/Hw] X 100
Y1= f (X1)
Md= [(100-Y1)/100] X Mw
Wherein Md represents the cut-off value of MCF of weld.